1. Field of the Invention
The present invention relates generally to an apparatus and method for chamfering a wafer, and more particularly to an apparatus and method for chamfering a periphery of a wafer.
2. Description of Related Art
A silicon ingot is sliced by a slicing machine into wafers, which are used for semiconductor devices. Then, the periphery of each wafer is chamfered in order to prevent the wafer from chipping, cracking, and so on. The wafer is chamfered by pressing a rotating grindstone against the periphery of the rotating wafer. A conventional chamfering apparatus moves the grindstone forward and backward, or vertically and horizontally with respect to the wafer to chamfer the periphery of the wafer.
The conventional chamfering apparatus, however, does not have sufficient stiffness because the grindstone rotates at a high speed during the chamfering, and it vibrates easily. Therefore, the machined surface of the wafer has coin marks, chipping, or the like.
The conventional chamfering apparatus relatively moves the wafer closer to the grindstone, which is rotating at the high speed (at a circumferential speed of 1000-3000 [m/min]). After grinding the wafer by a predetermined amount, the chamfering apparatus rotates the wafer slowly (at a circumferential speed of 0.6-3 [m/min]) to chamfer the whole circumference of the wafer. To reduce the machining time for one wafer, it is necessary to increase the circumferential speed of the wafer. To increase the circumferential speed of the wafer, the rotational speed of the grindstone must be increased, or the grindstone must have a relatively rough mesh. In the case that the rotational speed of the grindstone is increased, if a newly-attached grindstone is not well-balanced, the grindstone vibrates while rotating at a high speed. This causes defects on the machined surface of the wafer (coin marks, chipping, cracks, or the like). On the other hand, in the case that the grindstone has the relatively rough mesh, the grindstone grinds the wafer by a large amount, and thus, the wafer can be badly damaged. To address these problems, the diameter of the wafer is reduced by etching, or the diameter is reduced by gradually chamfering the wafer. These methods, however, require a long time.